The present invention relates to band saw machines, and in particular, to vertical cut off band saw machines with power tilting.
Vertical band saws with tilting frames and mechanisms and controllers for changing the angle of tilt have been available for a number of years. However, machines of this type are generally limited in the extent to which the frame can be tilted. In particular, tilting frame band saws with automated tilt mechanisms are generally limited to machines in which the maximum degree of tilt is plus or minus 45xc2x0. Examples of tilting frame band saws can be seen in U.S. Pat. No. 4,866,630; and in particular, FIG. 5 of the ""630 patent. Other examples of band saws with tilting frames can be seen in U.S. Pat. No. 4,658,689 and U.S. Pat. No. 5,878,644. Yet another style of vertical band saw with a hydraulic tilt mechanism can be seen in a brochure published by Armstrong-Blum Manufacturing Co. (copyright 1997) describing the MV Series of Medium Duty Vertical Production Band Saws of that company, the assignee of the present invention. In the MV Series brochure, the hydraulic tilt mechanism is comprised of a pair of cylinder actuators attached directly to the tilting frame which move the frame 45 degrees left and right of vertical.
Prior to the machine of the present invention, vertical band saws with controllable tilting frames were generally limited to tilting the frame a maximum of 45 degrees left and right of vertical. In addition, in machines such as the one described in the ""630 patent, the curved rack and pinion arrangement for moving the frame from one tilted position to another is relatively slow, complex and expensive, particularly in instances where there is a large movement of the frame called for by a particular sawing operation or when making a change from one operation to another. The difficulties of rapidly and accurately moving a vertical band saw frame from one position to another is particularly acute when the sweep of the band saw is increased to 60 degrees left and right of vertical.
Yet another example of a tilting frame vertical band saw is shown in U.S. Pat. No. 5,320,016. In the ""016 patent, the vertical frame is adjusted by the actuation of a cylinder actuator connected directly to the frame and a stationary support. Indeed, a common method of adjusting the position of a band saw frame in many contexts entails the use of a cylinder actuator directly mounted between the moveable frame and a stationary support. However, when undertaking the large movement associated with a frame capable of moving a frame with wide sweep, i.e., plus and minus 60 degrees from vertical or 120 degrees in total, a number of difficulties arise with the use of a simple hydraulic actuator. An arrangement in which there is a markedly non-linear relationship between the tilt angle of the frame and the displacement of the cylinder would require a complex controller in order to achieve accurate positioning of the frame. A high degree of non-linearity between tilt angle and actuator displacement would require a controller to cause the actuator to undergo varying displacements depending upon the position of the frame. Further, increasing the sweep of tilting frames with typical actuating mechanism is complicated by the varying length of the moment arm associated with the force required to move the frame from one position to another. The varying moment arm, and the resulting need for the application of varying forces, depending upon the angle of the frame, together with the complexity of a having to use an actuator in which different displacements are required, depending upon the location of the frame, have limited the development of band saws with wide sweep tilting.
The machine of the present invention addresses both the need for a tilting frame vertical band saw with a capability of being tilted 60 degrees to the left and right of vertical, and the need to have a mechanism which rapidly and accurately moves the frame from one position to another. The machine of the present invention accomplishes these advantages by the use of a combination of a tilt arm and a tilt drive in which the tilt arm has a first portion slidably connected to a tiltable frame, and a second portion which is pivotably connected to a support. The tilt drive, which may be a cylinder actuator or other drive mechanism, is pivotably mounted to a support and is slideably connected to the tilt arm. The tilt drive is preferably arranged so that the relationship between the degree of movement of the tilting frame and the displacement of the drive is generally linear over the entire sweep, i.e., from negative 60 degrees to positive 60 degrees from vertical.